The use of multiple channel cochlear prostheses to improve the communication abilities of profound/totally deaf patients is now an established procedure. Design improvements for these prostheses have been undertaken in the University of Melbourne's Department of Otolaryngology since 1970. The long term goal of the program is to achieve good speech discrimination without lip reading for a wide range of patients including children. The four specific aims of this grant proposal are as follows: (1) The first aim is to conduct psychophysical studies on profound/totally deaf patients who will be implanted with the receiver-stimulator, CI2, in the middle of 1987. CI2 is being developed under NIH Grant NS21027 ("An advanced multi-channel cochlear implant for deafness"; completion date: August 1987). It will produce simultaneous stimulation on three bipolar electrode pairs within a stimulus period (inverse of repetition rate). (2) The second aim is to monitor the changes in electrode impedance in patients following implantation by the telemetry system incorporated in the electronic design of CI2. (3) The third aim of this grant proposal is to develop a new receiver-stimulator, CI3, to enable research into the nature of the hearing sensations produced by electrical stimulation using different pulse rates on different electrode pairs, or alternatively the same rate on a large number (greater than three) of electrode pairs. CI2 and the existing receiver-stimulator, CI1, are not suitable for this research. (4) The fourth aim of this proposal is to undertake psychophysical studies on patients with CI3. The results of the psychophysical studies mentioned in (1) and (4) above will be used to direct the choice of the detailed structure and parameter values of the algorithms to be used in the speech processors for patients who will be implanted with CI2 or CI3. Loudness summation, electrode identification, repetition rate identification and synthetic vowel studies will be conducted. The development of the receiver-stimulator, CI3, will involve the design and layout of a single LSI CMOS integrated circuit to be fabricated under contract to VLSI Technology Ltd., Ca. The integrated circuit will be packaged into an implantable receiver- stimulator under contract to Cochlear Pty. Limited, Sydney.